The present invention relates to a magnetic disk device, and more particularly to a control method and a magnetic disk apparatus in which a magnetic head slider is retracted when the supply of an electric power from a power source is interrupted.
The conventional control method of retracting a magnetic head portion of a magnetic disk apparatus at the time of interruption of a power source includes a method disclosed by JP-A-7-211031. Namely, in the case where a head positioning actuator assembly is to be retracted at the time of interruption of power supply, the disclosed retracting method includes a step of charging a capacitor during a usual power source turn-on operation by a voltage which exceeds a power source voltage supplied to the magnetic disk apparatus, a step of discharging the stored current to the head positioning actuator assembly through the switching of the capacitor circuit at the time of interruption of power supply to the device, and a step of driving the actuator assembly to a predetermined position for retraction.
Also, JP-A-3-248379 has disclosed a method for stand-by driving of a magnetic head in which a back electromotive force from a member for driving the rotation of a magnetic disk is supplied to a magnetic head driving member at the time of stop of a magnetic disk driver to transport the magnetic head to a stand-by position at which the magnetic head or a magnetic head supporting member is engaged with a bearing member so that it mounts on (or gets on) the bearing member, thereby supporting the magnetic head on the bearing member in a state in which the magnetic head floats from the magnetic disk. The driving method includes a first step in which a voltage obtained by lowering the back electromotive force from the disk rotation driving member is supplied to the magnetic head driving member so that magnetic head is transported toward the stand-by position to bring the magnetic head into a state in which the magnetic head or the magnetic head supporting member contacts the bearing member but it does not mount on the bearing member, and a second step in which a voltage higher than the voltage supplied in the first step is supplied to the magnetic head driving member to bring the magnetic head or the magnetic head supporting member into an engagement with the bearing member so that the former mounts on the latter.
In the method disclosed by the JP-A-7-211031, a retraction operation is performed after the stop of supply of an electric power of the power source in such a manner that an electric power stored in the capacitor at the time of supply of the electric power is supplied to a magnetic head driving circuit. If this method is applied to a ramp type load/unload mechanism, there is a problem that a head or a head supporting portion impinges upon a ramp portion with a result that the head or the ramp portion is damaged.
In the method disclosed by the JP-A-3-248379, the retraction is made at the time of cut-off of a power source by performing the power supply in two steps by use of the back electromotive force of a rotating spindle motor. Namely, up to the front side of a lifter (or ramp), the magnetic head or the magnetic head supporting member is operated with a low voltage so that it impinges upon the lifter and is stopped. Thereafter, a high voltage is applied so that the magnetic head or the magnetic head supporting member ascends a ramp portion of the lifter.
In this case, the JP-A-3-248379 has stated that since there is employed a construction in which the application of the low voltage is continued immediately after stop of the power source, the magnetic head or the magnetic head supporting member impinges upon the lifter at a low speed. Practically the acceleration of the actuator is however continued so that the speed of the magnetic head or the magnetic head supporting member at the time of impingement thereof upon the ramp portion becomes high. As a result, it is also difficult to prevent the head from being damaged. In order to suppress the speed at the time of impingement to a tolerance, it is required that the voltage to be applied should be made considerably low.
An object of the present invention is to provide a magnetic disk apparatus of a retraction system using a high reliable ramp load type for reducing the ramp damage so that the speed of impingement on the ramp is made sufficiently low to allow the securely unloading retraction system when the power is even stopped supplying from a power source.
To attain the above object, a retracting method at the time of stop of supply of an electric power from a power source and a magnetic disk apparatus according to the present invention are characterized by comprising means for performing, at the time of stop of power supply from the power source, the supply of an electric power to an actuator assembly driving circuit in three separate steps with time differences therebetween.
A first aspect of the present invention lies in that there is provided means for performing a first power supply immediately after the interruption of supply of an electric power from a power source and performing the next power supply through the operation of a switch after the lapse of a fixed time from the first power supply.
A second aspect of the present invention lies in that there is provided means for detecting the arrival of an actuator assembly at an unload point (or the vicinity of a position at which the actuator assembly contacts a ramp). Immediately after the interruption of supply of an electric power from a power source, a first power supply is performed to a driving circuit of the actuator assembly. Thereafter, a switch is operated at the unload point (or the vicinity of the position of the actuator assembly contacting the ramp) so that the next power supply is started.
A third aspect of the present invention lies in that at the time of interruption of an electric power from a power source, a back electromotive force of a spindle motor is supplied to a head positioning actuator assembly in three separate steps with time differences therebetween.
A fourth aspect of the present invention lies in that means for storing an electric power during a usual power source turn-on operation is provided so that at the time of interruption of supply of an electric power from the power source, the stored electric power is supplied to a head positioning actuator assembly in three separate steps with time differences therebetween.